Skeletal muscle provides inspiration on how to achieve reversible, macroscopic, anisotropic motion in soft materials. Here we report on the bottom-up design of macroscopic tubes that exhibit anisotropic actuation driven by a thermal stimulus. The tube is built from a hydrogel in which extremely long supramolecular nanofibers are aligned using weak shear forces, followed by radial growth of thermoresponsive polymers from their surfaces. The hierarchically ordered tube exhibits reversible anisotropic actuation with changes in temperature, with much greater contraction perpendicular to the direction of nanofiber alignment. We identify two critical factors for the anisotropic actuation, macroscopic alignment of the supramolecular scaffold and its covalent bonding to polymer chains. Using finite element analysis and molecular calculations, we conclude polymer chain confinement and mechanical reinforcement by rigid supramolecular nanofibers are responsible for the anisotropic actuation. The work reported suggests strategies to create soft active matter with molecularly encoded capacity to perform complex tasks.

The ability to generate spiral ganglion neurons (SGNs) from stem cells is a necessary prerequisite for development of cell-replacement therapies for sensorineural hearing loss (SNHL). We present a protocol that directs human embryonic stem cells (hESCs) toward a purified population of otic neuronal progenitors and SGN-like cells. Between 82% and 95% of these cells express SGN molecular markers, they preferentially extend neurites to the cochlear nucleus rather than non-auditory nuclei, and they generate action potentials. The protocol follows an in vitro stepwise recapitulation of developmental events inherent to normal differentiation of hESCs into SGNs, resulting in efficient sequential generation of nonneuronal ectoderm, preplacodal ectoderm, early prosensory otic neuronal progenitors (ONPs), late ONPs, and cells with cellular and molecular characteristics of human SGNs. We thus describe the sequential signaling pathways that generate the early and later lineage species in the human SGN lineage, thereby better describing key developmental processes. The results indicate that our protocol generates cells that closely replicate the phenotypic characteristics of human SGNs, advancing the process of guiding hESCs to states serving inner-ear cell-replacement therapies and possible next-generation hybrid auditory prostheses.

Brain-derived neurotrophic factor (BDNF), a neurotrophin that binds specifically to the tyrosine kinase B (TrkB) receptor, has been shown to promote neuronal differentiation, maturation, and synaptic plasticity in the central nervous system (CNS) during development or after injury and onset of disease. Unfortunately, native BDNF protein-based therapies have had little clinical success due to their suboptimal pharmacological properties. In the past 20 years, BDNF mimetic peptides have been designed with the purpose of activating certain cell pathways that mimic the functional activity of native BDNF, but the interaction of mimetic peptides with cells can be limited due to the conformational specificity required for receptor activation. We report here on the incorporation of a BDNF mimetic sequence into a supramolecular peptide amphiphile filamentous nanostructure capable of activating the BDNF receptor TrkB and downstream signaling in primary cortical neurons in vitro. Interestingly, we found that this BDNF mimetic peptide is only active when displayed on a peptide amphiphile supramolecular nanostructure. We confirmed that increased neuronal maturation is linked to TrkB signaling pathways by analyzing the phosphorylation of downstream signaling effectors and tracking electrical activity over time. Furthermore, three-dimensional gels containing the BDNF peptide amphiphile (PA) nanostructures encourage cell infiltration while increasing functional maturation. Our findings suggest that the BDNF mimetic PA nanostructure creates a highly bioactive matrix that could serve as a biomaterial therapy in injured regions of the CNS. This new strategy has the potential to induce endogenous cell infiltration and promote functional neuronal maturation through the presentation of the BDNF mimetic signal.

Dynamic and reversible assembly of molecules is ubiquitous in the hierarchical superstructures of living systems and plays a key role in cellular functions. Recent work from the laboratory reported on the reversible formation of such superstructures in systems of peptide amphiphiles conjugated to oligonucleotides and electrostatically complimentary peptide sequences. Here, a supramolecular system is reported upon where exchange dynamics and host-guest interactions between -cyclodextrin and adamantane on peptide amphiphiles lead to superstructure formation. Superstructure formation with bundled nanoribbons generates a mechanically robust hydrogel with a highly porous architecture that can be 3D printed. Functionalization of the porous superstructured material with a biological signal results in a matrix with significant in vitro bioactivity toward neurons that could be used as a supramolecular model to design novel biomaterials.

The combination of biomaterials with stem cells is a promising therapeutic strategy to repair traumatic injuries in the central nervous system, and human bone marrow mesenchymal stem cells (BMSCs) offer a clinically translatable option among other possible sources of stem cells. We report here on the use of a supramolecular bioactive material based on a peptide amphiphile (PA), displaying a laminin-mimetic IKVAV sequence to drive neural transdifferentiation of human BMSCs. The IKVAV-PA self-assembles into supramolecular nanofibers that induce neuroectodermal lineage commitment after 1 week, as evidenced by the upregulation of the neural progenitor gene nestin (NES) and glial fibrillary acidic protein (GFAP). After 2 weeks, the bioactive IKVAV-PA nanofibers induce significantly higher expression of neuronal markers β-III tubulin (TUJ-1), microtubule-associated protein-2 (MAP-2), and neuronal nuclei (NEUN), as well as the extracellular matrix laminin (LMN). Furthermore, the human BMSCs exposed to the biomaterial reveal a polarized cytoskeletal architecture and a decrease in cellular size, resembling neuron-like cells. We conclude that the investigated supramolecular biomaterial opens the opportunity to transdifferentiate adult human BMSCs into neuronal lineage.